Crystalline Charge-transfer Complexes Research Articles

(Invited) Ion Transport in Solid-State Electrolytes Based on TTF - TCNQ Charge-Transfer Complexes

Current research on solid-state organic electrolytes mainly focuses on polymer electrolytes where ion transport is facilitated by chain segmental motion. The ionic conductivity of these polymer electrolytes at room temperature in too low for many practical applications. A limited number of prior reports suggest that solid-state electrolytes including organic crystalline charge-transfer complexes can have surprisingly high ionic conductivity. We report1 that processing and environmental conditions drastically impact electron and ion charge transport properties of charge-transfer complex electrolytes based on tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) mixed with lithium bis(trifluoromethylsulfonylimide) (LiTFSI). Thermal annealing and water vapor treatment decrease electronic conductivity and increase ionic conductivity. The electrolyte with 1-1-2-0.45 molar ratio of TTF-TCNQ-LiTFSI-H2O has an ionic conductivity of 2 × 10-3 S/cm at 25 °C with electronic conductivity of order 10-7 S/cm. Thermal annealing helps reduce connectivity of the charge-transfer complexes and expose more surfaces to interact with LiTFSI, thereby decreasing electronic conductivity. Exposure of the sample to water vapor then causes a substantial increase in ionic conductivity, even when the material remains in the solid state. In this presentation, we will also report on additional experimental studies of solid-state electrolytes incorporating TTF-TCNQ.Reference 1. L. Yang and J. L. Schaefer, “Water-Assisted Ion Conduction in Solid-State Charge-Transfer Complex Electrolytes for Lithium Batteries,” ChemRxiv, 2023. https://doi.org/10.26434/chemrxiv-2023-9k024

On the Morphology of a Discotic Liquid Crystalline Charge Transfer Complex

Discotic liquid crystalline (DLC) charge transfer (CT) complexes, which combine visible light absorption with rapid charge transfer characteristics within the CT complex, can have a great potential for photovoltaic applications when they can be made to self-assemble in a bulk heterojunction arrangement with separate channels for electron and hole conduction. However, the morphology of some liquid crystalline CT complexes has been under debate for many years. In particular, the liquid crystalline CT complex built from the electron acceptor 2,4,7-trinitro-9-fluorenone (TNF) and discotic molecules has been reported to have the TNF "sandwiched" either between the discotic molecules within the same column or between the columns within the aliphatic tails of the discotic molecules. We present a detailed structural study of the prototypic 1:1 mixture of the discotic 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) and TNF. Nuclear magnetic resonance (NMR) line widths and cross-polarization rates are consistent with the picosecond time scale anisotropic thermal motions of the HAT6 and TNF molecules previously observed. By computational integration of Rietveld refinement analyses of neutron diffraction patterns with density experiments and short-range structural constraints from heteronuclear 2D NMR, we determine that the TNF molecules are vertically oriented between HAT6 columns. The data provide the insight that a morphology of separate hole conducting channels of HAT6 molecules can be realized in the liquid crystalline CT complex.

Cis‐Specific Topochemical Polymerization: Alternating Copolymerization of 7,7,8,8‐Tetrakis(methoxycarbonyl)quinodimethane with 7,7,8,8‐Tetracyanoquinodimethane in the Solid State

From single crystal to single crystal: A crystalline charge-transfer complex of the title compounds underwent topochemical polymerization through a radical mechanism under UV irradiation or upon heating. This cis-specific solid-state copolymerization of the substituted quinodimethanes required the alternating monomers in the cocrystal to tilt (see picture).

ChemInform Abstract: Supramolecular Aggregation of m-Nitrobenzoic Acid by C-H×××O and O-H×××O Hydrogen Bondings in the Crystalline Charge-Transfer Complexes with Aromatic Hydrocarbons.

Charge-transfer complexation of m-nitrobenzoic acid (1) with aromatic hydrocarbons was found to exhibit size and shape selectivity: naphthalene or its 2,7-dimethyl and 2,3,6,7-tetramethyl derivatives failed to afford crystalline complexes with 1 whereas yellow crystals containing a stoichiometric amount of 2,3- or 2,6-dimethylnaphthalene, biphenylene, or anthracene were obtained by the direct method in CH2Cl2. X-ray analyses on these complexes have revealed dimer formation of 1 by O−H···O hydrogen bonding, yet the important structural motif observed as a common feature is the two-dimensional sheetlike network, in which the dimers of 1 are further connected by C−H···O hydrogen bonding to form a series of inclusion lattices that incorporate hydrocarbon guests. Such a supramolecular aggregation by C−H···O bonding was proven to take a significant part in the recognition properties of 1 to differentiate the dimethylnaphthalene isomers in its complexation process.

Acceleration of solid state Diels–Alder reactions by incorporating the reactants into crystalline charge transfer complexes

Diels–Alder reactions in a solid state between anthracene (AN) derivatives and p-benzoquinone (BQ) under mechanical stressing are accelerated by adding a catalytic amount of 2-naphthol (NP) or ( rac)-1,1′-bis-2-naphthol (BN). Their catalytic effects are based on the formation of the charge transfer complex with strong hydrogen bonds. BN is capable of incorporating BQ together with its reaction partner, AN derivatives, simultaneously. The resulted molecular complex with BN provides crystallographically ordered homogenic reaction fields, resulting in the higher rates of the present solid state Diels–Alder reaction.

Freezing of Crankshaft Motion of trans-Stilbene Molecule in Charge-Transfer Complexes, STB-TCNQ and STB-TCNQF4

Heat capacities of crystalline charge-transfer (CT) complexes between trans-stilbene (STB) and tetracyanoquinodimethane (TCNQ) or (TCNQ)F4 were precisely measured below room temperature by adiabatic calorimetry. Although orientational disorder is seemingly absent, a glass transition due to freezing of the crankshaft motion is observed in STB-(TCNQ)F4 around 240 K as in the case of highly disordered STB-TCNQ around 250 K. Assessment of the degree of CT by IR and structural methods indicates that STB-(TCNQ)F4 is not a fully but weakly (only partially) ionic complex with a similar degree of CT of 0.1−0.2 to that in STB-TCNQ, despite the large difference in acceptor ability.

EVIDENCES ABOUT CARBYNE FORMATION TOGETHER WITH OTHER CARBONACEOUS MATERIAL BY THERMAL DECOMPOSITION OF DIIODOACETYLENE

Carbonaceous matter containing carbyne has been synthesized by thermal decomposition of diiodoacetylene in boiling xylene or in o-dichlorobenzene. FT-IR and Raman spectroscopy together with powder x-ray diffraction were used to study the structure of the decomposition products and to identify the presence of carbyne domains. Together with carbyne domains, amorphous carbon was produced having residual iodine in its structure as shown by TGA-DTA. Additionally a crystalline charge-transfer complex between diiodoacetylene and o-dichlorobenzene has been identified. Thermodynamic calculations were performed in order to better understand the possible decomposition pattern from diiodoacetylene.

Supramolecular Aggregation of m-Nitrobenzoic Acid by C−H···O and O−H···O Hydrogen Bondings in the Crystalline Charge-Transfer Complexes with Aromatic Hydrocarbons

Charge-transfer complexation of m-nitrobenzoic acid (1) with aromatic hydrocarbons was found to exhibit size and shape selectivity: naphthalene or its 2,7-dimethyl and 2,3,6,7-tetramethyl derivatives failed to afford crystalline complexes with 1 whereas yellow crystals containing a stoichiometric amount of 2,3- or 2,6-dimethylnaphthalene, biphenylene, or anthracene were obtained by the direct method in CH2Cl2. X-ray analyses on these complexes have revealed dimer formation of 1 by O−H···O hydrogen bonding, yet the important structural motif observed as a common feature is the two-dimensional sheetlike network, in which the dimers of 1 are further connected by C−H···O hydrogen bonding to form a series of inclusion lattices that incorporate hydrocarbon guests. Such a supramolecular aggregation by C−H···O bonding was proven to take a significant part in the recognition properties of 1 to differentiate the dimethylnaphthalene isomers in its complexation process.

Solid-State Photodecarboxylation Induced by Exciting the CT Bands of the Complexes of Arylacetic Acids and 1,2,4,5-Tetracyanobenzene

Crystalline charge transfer complexes (3a, 3b, and 3c) of 1- and 2-naphthylacetic and 3-indoleacetic acid (1a, 1b, and 1c) with 1,2,4,5-tetracyanobenzene (2) were prepared by crystallization from the acetonitrile solutions. Irradiation of 3a and 3b gave methylnaphthalenes by decarboxylation and naphthyl(2,4,5-tricyanophenyl)methanes by subsequent dehydrocyanating condensation in the solid state. On the other hand, the photoreactivity of the crystal 3c was low; similar photoreaction occurred only at high temperature. These solid-state reactions are induced by exciting the CT bands of 3a and 3b. The product selectivities were different from those of the solution photoreaction. The relationships between the photoreactivities and the crystal structures of 3a and 3c are discussed.

Photoreactions of crystalline charge-transfer complexes

Abstract

The X-Ray Crystal Structure of a Charge-transfer Complex Derived from a Non-planar, Bulky, and Conformationally Flexible Donor Compound

Abstract Bis(9-hydroxyfluorenyl)-substituted dithienothiophene afforded a crystalline charge-transfer complex with 2,3-dichloro-5,6-dicyanobenzoquinone. The crystal structure was revealed by an X-ray analysis to be composed of a cage-like dimeric unit of the donor molecules which are alligned in a segregated columnar stack.

An Isomeric Series of Thiophene-Fused Tetracyanoquinodimethanes. I. Preparation and Physico-Chemical Properties

Abstract Four isomeric benzodithiophene analogs of 11,11,12,12-tetracyano-9,10-anthraquinodimethane have been prepared via a TiCl4 mediated condensation of the corresponding quinone and malononitrile. The reduction potential of these isomers was interpreted in terms of the resonance energies for the neutral and radical anion species. These new acceptor compounds, except for 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo[1,2-c:4,5-c′]dithiophene, formed crystalline charge-transfer complexes with tetrathiafulvalene, among which the complex of 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo[1,2-b:4,5-b′]dithiophene particularly exhibited a high room-temperature conductivity of 4.78 S cm−1.

Charge-carrier transport in heterogeneous conducting materials: Polymer + charge-transfer complex

The conductivity of reticulate doped polymers (i.e. conducting composites made of polymer matrix and of crystalline charge-transfer complex) shows only weak nonlinear and frequency-dependent effects. Such behavior cannot be explained neither by models describing charge-carrier transport in insulator-metal mixtures nor by fractal geometry. The conducting network appears to be truly continuous, made of ultrathin and very long molecular wires with properties characteristic of one-dimensional systems.

Analysis of the main parameters controlling the chargetransfer complex crystallization in the reticulate doping process

A comprehensive analysis of the charge-transfer (CT) complex crystallization in the reticulate doping process is presented. Our description enables to distinguish the main parameters controlling the CT complex crystallization conditions indispensable for obtaining highly conductive systems. The discussion concerns the role of the following parameters: temperature, solubility of the CT complex, solvent evaporation rate, initial thickness of the solution layer, polymer concentration, and the ratio of the mass of the CT complex to the mass of the polymer in the solution. The presented discussion of the influence of these parameters of the CT complex crystallization process is in good accordance with our studies of obtaining various conducting polymer/CT complex systems. The factors mentioned above have a strong hold on the morphology and the content of the crystalline CT complex, and hence on the electrical properties of reticulate doped systems.

Thermal investigation of organic crystalline complexes: II. Thermal behaviour of the complexes during heating

A number of crystalline charge-transfer complexes of polynuclear aromatic hydrocarbons with 2,4,6-trinitrotoluene (TNT) and picric acid were investigated by differential thermal analysis. It was found that the thermal behaviour of each complex during heating is different and depends mainly on its thermal stability. The temperatures, enthalpies and entropies of polymorphic transitions, and the melting points of eutectic mixtures were determined. It is suggested that every thermal investigation of the complexes should be based on other additional investigations such as thermal stability and solid-liquid phase diagrams.

Thermal investigation of organic crystalline complexes: I. Enthalpies and entropies of fusion

Melting points and enthalpies of a number of crystalline charge-transfer complexes (polynuclear aromatic hydrocarbons and some methyl substituted derivatives with 2,4,6-tri-nitrotoluene and picric acid) were determined by using differential thermal analysis. It was found that the determination of the enthalpy by the thermal analysis method is possible only for thermally stable complexes. For unstable complexes the value of enthalpy are somewhat lower than those expected for stable complexes.

Syntheses and Properties of 2,2′-Binaphtho[1,8-de]-1,3-dithiinylidene and Its Selenium Analog, 2-(1,3-Dithiol-2-ylidene)naphtho[1,8-de]-1,3-dithiin, and 2-(4H-Thiopyran-4-ylidene)naphtho[1,8-de]-1,3-dithiin

Abstract In order to discover new electron donors for conducting charge-transfer complexes, the four title compouds 1–4 composed of two heterocycles have been prepared via 1,8-dichalcogen-bridged naphthalene. The cyclic voltammetery indicates that symmetrical 1 and 2 are poor donors, but unsymmetrical 3 and 4 possess considerable donor abilities. The latter compounds are thus capable of forming some crystalline charge-transfer complexes with strong acceptors such as TCNQ, TCNQF4, and DDQ, which are, however, semi-conducting.

Molecular Complexes of Cyclophanes. XIV. Charge‐transfer complexes of polynuclear[2.2] paracyclophanes with π‐acceptors

AbstractThe charge‐transfer (CT) spectra of the π‐complexes formed by several π‐acceptors with some polynuclear[2.2]paracyclophanes have been measured. Comparison of these CT complexes with those of model compounds supports the existence of the transannular electronic interactions in the paracyclophane nucleus. The infrared spectra of a number of CT complexes reveal the increase of the electron density on the π‐acceptor molecule in the CT complexes. Some crystalline CT complexes were prepared and analysed.

ＴＣＮＱ誘導体の合成と性質

A powerful electron acceptor 7, 7, 8, 8-tetracyano-p-quinodimethane (TCNQ) and numerous organic electron acceptors with TCNQ backbone have been of great interest, as their crystalline charge-transfer complexes could be electrically conducting. This review describes the synthesis and physico-chemical properties of TCNQ compounds synthesized until now. The extension of π-conjugation and the incorporation of heteroatoms within the molecular framework have been used for the major structural modification of TCNQ. Redox properties are recorded in appropriate tables.

Charge Transfer Complexes of Nickel Dithiolenes with Methyl Viologen

Abstract Charge-transfer Complexes, Nickel Dithiolenes. Methyl Viologen, X-Ray Anionic nickel dithiolenes form crystalline charge-transfer complexes with methyl viologen in its oxidized and reduced forms. X-ray analysis reveals that the planar acceptor methyl viologen interacts with the planar dithiolene donor via an expected parallel and a novel perpendicular arrangement.